This invention relates to methods and apparatus for providing quality measurements for voice equipment under test, and more particularly to methods and apparatus for providing real-time objective perceptual quality measurements of voice or audio signals received by such equipment.
Voice quality evaluation is a difficult task for speech systems, especially those involving compression and coding, because common waveform and spectrum similarity criterion do not correlate particularly well with perceived quality of received voice signals. Formerly, voice quality evaluation of telecommunication systems have been measured off-line using formal perceptual listening tests that are performed in a carefully controlled environment, using pre-prepared voice material. Although this practice is effective, it is both costly and time consuming. In addition, results obtained from such tests are dependent upon the individual test subjects and their environment. As a result, findings from such tests are not always repeatable or consistent.
Recent research in the field of psycho-acoustics has led to a better understanding of how human beings perceive voice and sounds. By applying some of the findings of this field, such as critical band theory, auditory masking, and perceptual loudness, etc., it is now possible to develop xe2x80x9cobjectivexe2x80x9d speech measures that closely match results of formal subjective listening tests. Various organizations, including, for example, the International Telecommunications Union (ITU), have developed algorithms to measure voice quality off-line using files stored in a computer. Examples of known objective measurement algorithms are Perceptual Speech Quality Measure (PSQM), Measuring Normalizing Blocks (MNB), Perceptual Analysis Measurement System (PAMS), and Modified Bark Spectral Distortion (MBSD) measure. The latter measurement, for example, splits frequencies into bands that reflect human auditory reception.
Known objective perceptual quality measurement systems require measurement of voice quality to be done off-line, i.e., from stored, received voice data. It would be desirable if such objective perceptual quality measurements could be made in real time or near real time in operational equipment.
The present invention, in one aspect, is a method for providing real-time perceptual quality measurements of an audio signal. A quality test signal, including an audio test signal, is received by equipment under test. Playback of a pre-stored representation of the audio signal is coarsely synchronized to the received audio test signal, for example, utilizing a synchronizing pulse in a header of the quality test signal. The playback is then finely synchronized to the received audio signal, for example, by comparing data in a windowed portion of the received audio test signal and a windowed portion of the pre-stored representation of the audio test signal and by adjusting a windowed portion of the pre-stored representation of the audio test signal in accordance with results of the comparison. A window of the received audio test signal is then compared to a portion of the finely synchronized playback of the pre-stored representation of the audio test signal to output a quality measurement of the received audio test signal.
In another aspect, the invention comprises an audio quality analyzer (AQA) to evaluate quality of a quality test signal received by equipment under test, where the quality test signal includes an audio test signal. The AQA is configured to coarsely synchronize playback of a pre-stored representation of the audio test signal to the received audio test signal, to finely synchronize playback of said pre-stored representation of the audio test signal to the received audio test signal and to compare a window of the received audio test signal to a portion of the finely synchronized playback of the pre-stored representation of the audio test signal to output a quality measurement of the received audio test signal.
Accordingly, it will be seen that the invention provides objective perceptual quality measurements of audio and voice signals in real time or near real time in operational equipment.